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Antistatic rubber principle

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Rubber is an electrically insulating material, and when its surface is rubbed, the charge in a static state accumulates to form static electricity. When static electricity accumulates to a certain amount, it is released in the form of a spark. If the amount of discharge is slight, it will not pose a hazard to the human body, but when the discharge reaches a certain level, it will cause an electric shock. In order to protect personal safety, the rubber used in this case must be an antistatic rubber that can remove static electricity. The dangers caused by static electricity are roughly the following:


1 When static electricity is released, if there is fire, flammable or explosive materials around, it will cause fire;


2 Injury to the human body, although this kind of electric shock is not fatal, it is always harmful to the human body;


3 The surface with static electricity will absorb the surrounding dust. For example, when the skin of a textile mill draws a yarn, static electricity is generated between the yarn and the yarn due to friction. When the static electricity accumulates to a certain extent, it will adsorb the flying yarn in the surrounding air and affect the operation.


In short, the exact definition of antistatic is not to prevent the generation of static electricity, but to remove the static electricity that has accumulated.


(1) Resistivity of rubber


The electrical insulation capability of rubber is conventionally characterized by resistivity (unit: Ω ∙ CM), where the range of 104〜7Ω ∙ CM is used as the semiconductor rubber, which is greater than this as the insulating rubber, and less than this is the conductive rubber. All kinds of rubber have good electrical insulation properties. In contrast, neoprene and nitrile rubber have the lowest resistivity and are called “semiconductor rubber”. They are often used as the first choice for antistatic, but they are not the only consideration. The object can be adjusted by adding an antistatic agent.



Wide application of several underwater acoustic rubber

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Underwater detection by sound wave transmission, reflection, transmission and attenuation, or removal
The rubber products for the purpose of noise are collectively referred to as underwater acoustic rubber. Rubber as a polymer is widely used in this field due to its damping property.

In the military, water and underwater ships use underwater acoustic rubber to monitor and identify the location of enemy ships, or to conceal themselves. In economic construction, it is used to probe submarine deposits, especially oil and gas. In addition, it is used to determine the location of shipwrecks and salvage shipwrecks, and to track fish stocks during fishing operations.

Under the function of water acoustic rubber, it can be divided into noise reduction, anti-sound and sound transmission. Among them, anti-sound and sound-transparent rubber are used to locate enemy ships, which is called “active sonar.” That is, the party engaged in the war determines the orientation and movement of the enemy submarine by means of underwater acoustic rubber. In addition, underwater ships, such as submarines, can also use noise-reducing rubber to reduce their own underwater noise, to avoid the search and tracking of enemy anti-submarine ships and anti-submarine aircraft, thus preventing target exposure and shielding and protection. This is called “passive sonar.”

The manufacturing points of several underwater acoustic rubbers are briefly described below.

(1) Silencing rubber

The main material should be selected from the characteristic acoustic impedance (the product of the rubber density and the propagation speed of the acoustic wave in the rubber) matching (close to) the acoustic impedance of the propagation medium (water). The preferred host materials are butyl rubber and nitrile rubber. Some bubble-like fillers such as cork powder and mica powder can be added to the rubber compound to enhance the sound absorption effect.

(2) Soundproof rubber

It is mainly used for the sound-permeable window of the shroud and the transducer of the sonar. The suitable rubber types are natural rubber, neoprene, butyl rubber and urethane rubber. Their sound transmission coefficient can reach more than 90%. In addition to being used to detect submarines, sound-permeable rubber can also detect mines. It can be used to detect submarine oil and gas fields in civilian use. Performance requirements are high sensitivity to water, sound and signal transmission, ie no distortion. It is also required that the characteristic acoustic impedance of the rubber used matches the characteristic acoustic impedance of the water. Natural rubber, neoprene, butyl rubber and urethane rubber are preferred for the rubber used.

(3) Anti-sound rubber

Used to eliminate and reduce noise interference. The focus of the formulation design is that the characteristic acoustic impedance of the rubber and the characteristic acoustic impedance of the water are large, and the rubber is required to have a microporous structure. There is air in the micropores. When the air content is greater than 50%, the shear modulus decreases and the wave velocity decreases, which results in high reflectivity at the interface between the foam and water. When the reflection coefficient is greater than 80%, it is effective. Eliminate the flow of water and the noise emitted by the device itself.

Rubber synchronous toothed belt manufacturing process

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It is divided into two types: molding method (using dry glue as raw material) and casting method (using liquid polyurethane as raw material).


(1) Molding method


1) The main raw material rubber is mainly neoprene, and the reinforcing layer is usually made of steel wire rope or aramid rope. Requirements for strong ropes include high elongation, low elongation and low thermal deformation.
2) Two methods of forming parting and forming drum:
The mold method is divided into five steps, the first step, the patch cloth (lapped with 45° obliquely); the second step, the embedded rack; the third step, the winding rope, the single tension requirement reaches 78-100N; Four steps, filming, with a 0.5mm thick film multi-layer package to the specified thickness; the fifth step, add the outer hoop, put it into the vulcanization tank for vulcanization.
The forming drum method is carried out on a single drum forming drum. First, attach the hanging tape to the forming drum, wrap the wire rope, and attach a layer of tape to complete the forming of the embryo.


（3) Vulcanization in two ways.


a. The iron hoop pressure vulcanization is suitable for the semi-finished product formed by the die method, pressurized by the iron hoop, and then vulcanized by placing it in a vulcanization tank or a flat press.
b. The rubber sleeve vulcanization is suitable for the forming of the drum formed by the drum. The embryo with the forming drum is sleeved on the rubber sleeve and sent to the vulcanization tank, and simultaneously pressurized and heated inside and outside. The first stage is 0.3~0.4MPa vapor pressure, which is maintained for 2~3min; the second stage is further pressurized to 0.8~1MPa, and continues to the specified curing cycle.


(2) pouring method


Polyester polyurethane is used as the main material and is completed in four steps.
1 Polycondensation is carried out by using adipic acid and ethylene glycol as raw materials to obtain a dihydroxy-terminated polyester.
2 Add toluene diisocyanate to the polyester and extend the chain to form a prepolymer.
3 Vacuum and defoam the prepolymer.
4 Add the curing agent MOCA, stir evenly, and pour into the cavity with the strength layer preset. After heating, solidifying and demoulding, the finished product is obtained.


application


The synchronous toothed belt is thin and strong, and is resistant to flexing. Therefore, the transmission speed is high and the transmission efficiency is high, up to 100 kW. It is used to replace the chain or gear transmission, which can reduce noise and save lubricating oil. Therefore, it is widely used in precision machine tools, computers, chemical fiber machinery, textile machinery, automotive transmission systems and general machinery.

Sectional classification of V-belts

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The V-belt is a large class of transmission tapes. It is named after the isosceles trapezoidal section. It has developed rapidly since the advent of the last century and can replace mechanical gear transmissions. The V belt is widely used for power transmission of electric motors and internal combustion engines. This is because it is continuously improved in terms of material, structure and shape, and combines many advantages such as high power, high speed, small deformation, long life and small space.

With the diversification of the use requirements, the classification of V-belts is also increasing day by day. According to the belt structure, there are edging and trimming points; according to the core structure, there are disc cores and wire cores; depending on the application, there are industries. , the agricultural machinery industry and the automotive industry; according to the shape of the broken (cut) face, there is a wide and narrow difference. According to the shape of the section, it can be divided into the following three types.


(1) ordinary V belt


The ratio of the section height/top section width of the ordinary V-belt is 0.7, and the wedge angle is 40°, which is suitable for general mechanical transmission, but is not suitable for use in automobiles and agricultural machinery. It consists of a top coat, a top coat, a strong (stretch) layer (raw curtain or cord) and a primer (compressed) layer (see Figure 6·IO). O strength layer material is divided into two types: wire and cord. The advantages of the wire structure include relatively high flexibility, no quality problems such as interlayer displacement and delamination, but the wire rope V-belt of the same specification is not as strong as the V-belt of the cord. The section specifications are divided into 0, A.E, C, D, E, F and other models from small to large.
All kinds of V belts can be made into a single root, that is, the molding to vulcanization is carried out separately, which is called a cloth type; or the cylindrical shaped embryo can be formed first, and then vulcanized and then cut into a single root, which is called a cutting belt. From the appearance, the entire body of the former is covered with a cloth without being exposed, and the sides of the latter are exposed. The production efficiency of the dicing tape is high, but the reinforcing layers on both sides are exposed, and the fiber ends are prone to disorder.


(2) Narrow V-belt

Multi-ribbed belt outline drawing


The shape parameters of the section are different from those of the ordinary: the aspect ratio of the section is 0·9, which is higher than 0.2 of the ordinary V-belt, and the appearance is obviously narrow.
This structural feature gives it the following performance characteristics:
1 higher transmission power, 0.5-1.5 times higher than the V-belt of the common structure;
2 The structure is compact and 50% smaller than the ordinary structure;
3 line speed is high, up to 40~50m∕s, suitable for high speed operation;
4 The center distance of the transmission wheel and the width of the wheel groove can be reduced to make the overall transmission system more compact.


(3) Wide V belt

Schematic diagram of the narrow V-belt


The wide V-belt refers to a flat V-belt with a height/width ratio of only about 0.3. It is usually used in a belt-type transmission. Therefore, it is also called a variable-speed V-belt, which is developed rapidly due to smooth transmission, convenient maintenance, and low manufacturing cost. In order to meet the needs of shifting, the top and bottom surfaces can also be toothed to improve the engagement with the drive wheel.